Fix build reproducibility in Make 3.82

Make 3.82 no longer sort the result of wildcards (see
http://comments.gmane.org/gmane.comp.gnu.make.bugs/4260

). This may break
build reproducibility.

This patch sort results of wildcards to ensure reproducibility.

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>